The invention lies in the field of paper handling devices and pertains, more specifically, to a system in the infeed of a web-fed printing machine for controlling the tension on the web.
The infeed in a printing machine is disposed between a reelstand, which holds a reel with a continuous web, and the following printing units. The function of the infeed is to maintain proper web tension in the printing units and to correctly align the paper web. Web tension is adjusted in the infeed with so-called dancer rollers disposed between the pull rollers, which pull the paper web from the reel, and the printing units. One of more web tension measuring rollers are disposed to measure the web tension at all times. Besides the primary pulling forces, the web tension is subject to variations due to differences in the elasticity of the paper web, the relative humidity, faults in the web unwinding from the reel, or splicing.
Existing infeed configurations are maximized to maintain a constant web tension. Since tension is defined as the ratio of the pulling force to the cross-sectional area of web, the strain on the web varies with the caliper of the web materialxe2x80x94even if the pulling force remains constant. For some processes it is desirable to maintain a constant strain in the web. Current infeed configurations which maintain constant web tension are not equipped to measure web strain and to maintain a constant web strain.
It is accordingly an object of the invention to provide a strain control system for a web-fed printing machine, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which enables web strain control and which allows a constant strain to be maintained on the infeed web.
With the foregoing and other objects in view there is provided, in accordance with the invention, a strain control configuration in a web-processing machine, comprising:
a reel carrying a continuous web of material and disposed to rotate for paying out the web and feeding the web to a process;
a measuring device for measuring a caliper of the web material;
a tension setting device for setting a tension of the web entering the process; and
a drive circuit connected to the measuring device and to the tension setting device, the drive circuit controlling the tension of the web via the tension setting device in dependence on the caliper of the web material to maintain a substantially constant strain on the web.
In other words, some processes are improved if a constant strain is set on the web instead of constant tension. The novel system measures the caliper of the web material and adjusts the tension to achieve the desired constant strain. The caliper may be measured by monitoring the radius of the expiring web reel in connection with the angular position of the reel. The web caliper is input into a control scheme that includes an algorithm determining the appropriate tension to applied to the web in accordance with its caliper. The control scheme outputs a variable force command to a dynamic dancer which adjusts the web tension and thus sets the constant web strain.
In accordance with an added feature of the invention, the measuring device comprises a sensor disposed to measure a diameter of the reel and a sensor for sensing an angular position of the reel.
In accordance with an additional feature of the invention, the tension setting device includes a dancer roller about which the web is deflected and a device for controlling a position of the dancer roller for selectively increasing and decreasing a deflection of the web between the reel and the process.
In accordance with another feature of the invention, the tension setting device further includes a piston/cylinder assembly operatively connected to the dancer roller and a pressure regulator communicating with the piston/cylinder assembly for adjusting a position of the dancer roller.
The variable force may be injected via an air cylinder, a hydraulic cylinder, a spring with a dynamic ground, or an electromagnetically driven actuator.
In accordance with a further feature of the invention, the drive circuit is configured to calculate the caliper of the web material and programmed to adjust the tension of the web in dependence on the caliper to maintain a substantially constant strain on the web.
In accordance with again an added feature of the invention, the drive circuit is configured to adjust the strain on the web to a desired strain set at a given input of the drive circuit.
In accordance with again an additional feature of the invention, the drive circuit comprises a processor for calculating a desired tension required to maintain the substantially constant strain on the web, and a first converter for converting a signal representing the desired tension to a signal representing a force to be applied to the web.
In accordance with again a further feature of the invention, the drive circuit further comprises a second converter connected to the first converter for converting the signal representing the force to a signal representing a pressure to be applied to a pressure regulator defining the tension on the web.
In accordance with a concomitant feature of the invention, the drive circuit further comprises a feedback loop for iteratively correcting and driving an output signal thereof to a desired strain set at an input thereof.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a strain control in a web-fed printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of the specific embodiment when read in connection with the accompanying drawings.